In recent years, in a data storage device such as hard disc drives (HDDs), technologies which prevent recorded data from being read by a third party are commonly used. For example, in order to prevent recorded data from being read after discarding a data storage device, a process causing the recorded data to be unreadable is performed before the data storage device is discarded. As such a method, a method of physically destroying the data storage device, or a method of recording a specific pattern (for example, a pattern of all zeros) in all recording regions and overwriting recorded data (erase processing) are typically used. When considering reusing the data storage device, the latter method is applied. However, a method of determining whether an erase process has been reliably executed with respect to a data storage device after the erase process is complete is not currently known in the art.